There are many applications for molded plastic structures, such as benchtop or tabletop panels, which require lightweight yet high strength structures and which structures should be provided in so-called standard dimensions. Benchtop panels are usually of rectangular configuration with lengths and widths in predetermined dimensional units, such as four feet by two feet, etc., but which also should be modifiable to be of reduced widths or lengths. There has also been a need to provide such panels which may be easily mounted on and connected to a frame or substructure. All of the above-mentioned desiderata are difficult to meet in prefabricated panels, particularly panels formed of injection molded plastics, or the like. However, the present invention does provide advantages and desired features in prefabricated benchtop panels as will be appreciated by those skilled in the art.